Behavior of fixed offshore  wind substructures

In this research, simplified finite element models for monopile and jacket offshore wind turbines are established for dynamic response analysis based on the National Renewable Energy Laboratory’s 5 MW offshore wind turbine model. 

For a fair comparison, a number of design constraints are applied. The same turbine, tower structure, and transition piece configuration are used. The same external environmental conditions (wind-wave-current loading) are maintained. The same standards are used in order to satisfy the ULS, FLS, and SLS requirements. Additionally, the natural frequencies of the two models are almost identical.

Tower top displacement and member stress of two kinds of offshore wind turbine models with fixed and flexible bases are analyzed using the pile-soil interaction module of X-WIND. 

A parametric study is conducted to evaluate the sensitivity of the dynamic responses to the changes in environmental conditions, soil properties and pile embedded lengths. 

The dynamic responses of the JOWT are more largely affected by the changes in the soil property and pile embedded length, especially in terms of the tower top F-A displacement. 

The dynamic responses of the MOWT are more sensitive to the changes in environmental conditions(wave direction).  

Although the JOWT is more sensitive to the changes in soil property and pile embedded length, its structural dynamic responses are always smaller than those of the MOWT. Overall, the JOWT performs better than the MOWT in transitional waters.